In general, data is transmitted and received between two opposed transmitter-receivers via transmission media. FIG. 1 is a diagram showing an example of optical transmitter-receivers that transmit and receive optical signals through optical fibers as transmission media. In FIG. 1, optical transmitter-receivers 101 and 102 are connected via optical fibers 103 and 104 with each other. Electrical signals output from or input to the optical transmitter-receivers 101 and 102 are sent to or from other equipment such as telecommunication equipment and electronic information processing equipment (not shown). The optical transmitter-receiver 101 (102) converts an electrical signal fed from other equipment to an optical signal and transmits the optical signal to the optical transmitter-receiver 102 (101), or converts an optical signal received from the transmitter-receiver 102 (101) to an electrical signal to send other equipment the electrical signal.
With regard to the data rate or transmission rate, data format and the like, various standards have been defined in order to facilitate the interconnection between transmitter-receivers. As an example of such standards may be cited the IEEE 802.3ae 10GBASE-LR standard defined by an international standards association, IEEE SA (Institute of Electrical and Electronics Engineers Standard Association). The standards specify, for example, the data rate (10.3125 Gbps on optical fiber), wavelength of light, data format, and transmission distance.
As a conventional technique for surely conducting optical communication, Japanese Patent Application laid open No. 2000-68938 has disclosed “Optical Transmitter-Receiver”. The optical transmitter-receiver at the transmitting end sends a signal to a channel and learns the status of optical fiber by monitoring the return signal. The information is fed back to the intensity of a laser beam.
The conventional optical transmitter-receiver, however, has some problems. First, the transmitter-receiver does not have a function for automatically setting the transmission rate according to the status of a channel or the like. Consequently, it is required to set the transmission rate manually according to the status of a channel including the loss of optical fiber measured with an additional measuring instrument. Besides, in the case where the transmission rate is fixed and cannot be changed, the transmitter-receiver itself has to be replaced with another model.
In the following, a description will be made of problems caused by the fixed transmission rate by taking an optical transmitter-receiver based on the aforementioned 10GBASE-LR standard as an example. Generally, in digital signal communications, data can be transmitted and received with lower power as the transmission rate decreases. For that reason, if there is a considerable loss in a transmission medium such as optical fiber, it is possible to transmit and receive data. In the case of a 10GBASE-LR standard-based optical transmitter-receiver, however, the transmission rate is fixed at 10.3125 Gbps. Therefore, when the transmission loss is increased to a certain value, the optical transmitter-receiver is disabled for communication. In other words, even when data can be communicated by reducing the transmission rate, the optical transmitter-receiver cannot adjust a transmission rate setting because of the fixed transmission rate.
Second, the conventional transmitter-receiver does not have a function for automatically setting output power according to the status of a channel or the like. As in the case of the transmission rate described above, it is required to set output power manually according to the status of a channel including the loss of optical fiber measured with an additional measuring instrument. In the case where output power is fixed and cannot be changed, the transmitter-receiver itself or the interface thereof has to be replaced with another model.
Third, the conventional transmitter-receiver does not have a means for determining the status of a transmission medium such as the loss of optical fiber. Therefore, as described above, it is required to determine the status of a channel including the loss of optical fiber with an additional measuring instrument prior to connecting transmitter-receivers. For this reason, the renewal of the transmitter-receiver requires a considerable time, and also it is difficult to modify system configuration.